2,586 research outputs found
A close look into an intermediate redshift galaxy using STIS
We present a detailed view of a galaxy at z=0.4 which is part of a large
database of intermediate redshifts using high resolution images. We used the
STIS parallel images and spectra to identify the object and obtain the
redshift. The high resolution STIS image (0.05'') enabled us to analyse the
internal structures of this galaxy. A bar along the major axis and hot-spots of
star formation separated by 0.37'' (1.6 kpc) are found along the inner region
of the galaxy. The analysis of the morphology of faint galaxies like this one
is an important step towards estimating the epoch of formation of the Hubble
classification sequence.Comment: Astronomy and Astrophysics Letter - accepte
Interference pattern in the collision of structures in the BEC dark matter model: comparison with fluids
In order to explore nonlinear effects on the distribution of matter during
collisions within the Bose-Einstein condensate (BEC) dark matter model driven
by the Schr\"odinger-Poisson system of equations, we study the head-on
collision of structures and focus on the interference pattern formation in the
density of matter during the collision process. We explore the possibility that
the collision of two structures of fluid matter modeled with an ideal gas
equation of state also forms interference patterns and found a negative result.
Given that a fluid is the most common flavor of dark matter models, we conclude
that one fingerprint of the BEC dark matter model is the pattern formation in
the density during a collision of structures.Comment: 7 pages, 22 eps figure
Scalar Field Dark Matter: behavior around black holes
We present the numerical evolution of a massive test scalar fields around a
Schwarzschild space-time. We proceed by using hyperboloidal slices that
approach future null infinity, which is the boundary of scalar fields, and also
demand the slices to penetrate the event horizon of the black hole. This
approach allows the scalar field to be accreted by the black hole and to escape
toward future null infinity. We track the evolution of the energy density of
the scalar field, which determines the rate at which the scalar field is being
diluted. We find polynomial decay of the energy density of the scalar field,
and use it to estimate the rate of dilution of the field in time. Our findings
imply that the energy density of the scalar field decreases even five orders of
magnitude in time scales smaller than a year. This implies that if a
supermassive black hole is the Schwarzschild solution, then scalar field dark
matter would be diluted extremely fastComment: 15 pages, 21 eps figures. Appendix added, accepted for publication in
JCA
Internal Kinematics of Luminous Compact Blue Galaxies
We describe the dynamical properties which may be inferred from HST/STIS
spectroscopic observations of luminous compact blue galaxies (LCBGs) between
0.1<z<0.7. While the sample is homogeneous in blue rest-frame color, small size
and line-width, and high surface-brightness, their detailed morphology is
eclectic. Here we determine the amplitude of rotation versus random, or
disturbed motions of the ionized gas. This information affirms the accuracy of
dynamical mass and M/L estimates from Keck integrated line-widths, and hence
also the predictions of the photometric fading of these unusual galaxies. The
resolved kinematics indicates this small subset of LCBGs are dynamically hot,
and unlikely to be embedded in disk systems.Comment: To appear in "Starbursts: from 30 Doradus to Lyman Break Galaxies"
2005, eds. R. de Grijs and R. M. Gonzalez Delgado (Kluwer
On the Space Time of a Galaxy
We present an exact solution of the averaged Einstein's field equations in
the presence of two real scalar fields and a component of dust with spherical
symmetry. We suggest that the space-time found provides the characteristics
required by a galactic model that could explain the supermassive central object
and the dark matter halo at once, since one of the fields constitutes a central
oscillaton surrounded by the dust and the other scalar field distributes far
from the coordinate center and can be interpreted as a halo. We show the
behavior of the rotation curves all along the background. Thus, the solution
could be a first approximation of a ``long exposition photograph'' of a galaxy.Comment: 8 pages REVTeX, 11 eps figure
Shape coexistence in Lead isotopes in the interacting boson model with Gogny energy density functional
We investigate the emergence and evolution of shape coexistence in the
neutron-deficient Lead isotopes within the interacting boson model (IBM) plus
configuration mixing with microscopic input based on the Gogny energy density
functional (EDF). The microscopic potential energy surface obtained from the
constrained self-consistent Hartree-Fock-Bogoliubov method employing the
Gogny-D1M EDF is mapped onto the coherent-state expectation value of the
configuration-mixing IBM Hamiltonian. In this way, the parameters of the IBM
Hamiltonian are fixed for each of the three relevant configurations (spherical,
prolate and oblate) associated to the mean field minima. Subsequent
diagonalization of the Hamiltonian provides the excitation energy of the
low-lying states and transition strengths among them. The model predictions for
the level energies and evolving shape coexistence in the considered
Lead chain are consistent both with experiment and with the indications of the
Gogny-EDF energy surfaces.Comment: 12 pages, 6 figures, 1 tabl
The end-to-end testbed of the Optical Metrology System on-board LISA Pathfinder
LISA Pathfinder is a technology demonstration mission for the Laser
Interferometer Space Antenna (LISA). The main experiment on-board LISA
Pathfinder is the so-called LISA Technology Package (LTP) which has the aim to
measure the differential acceleration between two free-falling test masses with
an accuracy of 3x10^(-14) ms^(-2)/sqrt[Hz] between 1 mHz and 30 mHz. This
measurement is performed interferometrically by the Optical Metrology System
(OMS) on-board LISA Pathfinder. In this paper we present the development of an
experimental end-to-end testbed of the entire OMS. It includes the
interferometer and its sub-units, the interferometer back-end which is a
phasemeter and the processing of the phasemeter output data. Furthermore,
3-axes piezo actuated mirrors are used instead of the free-falling test masses
for the characterisation of the dynamic behaviour of the system and some parts
of the Drag-free and Attitude Control System (DFACS) which controls the test
masses and the satellite. The end-to-end testbed includes all parts of the LTP
that can reasonably be tested on earth without free-falling test masses. At its
present status it consists mainly of breadboard components. Some of those have
already been replaced by Engineering Models of the LTP experiment. In the next
steps, further Engineering Models and Flight Models will also be inserted in
this testbed and tested against well characterised breadboard components. The
presented testbed is an important reference for the unit tests and can also be
used for validation of the on-board experiment during the mission
Collective structural evolution in neutron-rich Yb, Hf, W, Os and Pt isotopes
An interacting boson model Hamiltonian determined from
Hartree-Fock-Bogoliubov calculations with the new microscopic Gogny energy
density functional D1M, is applied to the spectroscopic analysis of
neutron-rich Yb, Hf, W, Os and Pt isotopes with mass .
Excitation energies and transition rates for the relevant low-lying quadrupole
collective states are calculated by this method. Transitions from prolate to
oblate ground-state shapes are analyzed as a function of neutron number in
a given isotopic chain by calculating excitation energies, (E2) ratios, and
correlation energies in the ground state. It is shown that such transitions
tend to occur more rapidly for the isotopes with lower proton number , when
departing from the proton shell closure Z=82. The triaxial degrees of freedom
turn out to play an important role in describing the considered mass region.
Predicted low-lying spectra for the neutron-rich exotic Hf and Yb isotopes are
presented. The approximations used in the model and the possibilities to refine
its predictive power are addressed.Comment: 12 pages, 7 figures, 1 table, accepted for publication in Phys. Rev.
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